The New England Patriots, as every football fan knows, are a perfect 17–0. They are also the second best team in the NFL. The best team is their opponent this Sunday for the championship of the AFC, the San Diego Chargers. Okay, I just said that to get your attention. If I have it, let me show you what an interesting case can be made to support that statement.

The strength of a Super Bowl contender when it reaches the postseason is almost always gauged by its performance in the second half. Not to belabor the point, but everyone should recall the obvious example of last year’s Chicago Bears, whose miserable second half presaged their Super Bowl flop against the Colts. Clearly, if the Patriots are compared to the Chargers on the basis of season-long performance, it’s no contest. Over the course of the regular season, the 2007 Patriots were possibly one of the most dominant teams in NFL history — and the Chargers just another good team.

No lengthy chart is needed to make this case — a few simple statistics suffice. New England, with its playoff victory over Jacksonville last Sunday, has won 17 straight games. San Diego, with its stunning upset of defending champion Indianapolis, is now 13–5.

The Patriots have averaged 11 more points per game than the Chargers, 36.8 (first in the league) to 25.8 (fifth best). In the most important indicator of offensive power, yards per pass, New England is first at 8.3, while San Diego is a distant 19th at 6.7.

And yet, the Chargers, who were a mediocre team through their first 10 games (5–5), have come out of nowhere in perhaps the greatest late-season surge seen so far in this decade. Because of their history of spectacular tank jobs (most notably, their mystifying loss to New England in last year’s divisional playoff and their underachieving start this year), practically no one, myself included, noticed how improved they were by the end of this season.

How good are the Chargers? Let’s compare them to the Patriots over the last eight games, including playoffs:

The similarity between the numbers of the two teams is eye-opening. What’s even more eye-opening is the Chargers’ superiority in several key statistics, most notably in yards per pass allowed on defense and defensive points allowed, where they are nearly six points a game better than the Patriots. The Chargers have averaged 4.6 fewer points per game on offense, but that’s mostly because they run more plays on the ground (New England’s pattern is to pass late in the game and pile up more points; San Diego’s is generally to keep the ball on the ground and eat up the clock). The bottom line is that over their last eight games, the Chargers have won by an average of 15.4 points compared to the Patriots’ 14.2.

Here are more eye-openers: Over the course of the season, the two teams rushed the passer with about the same effectiveness, the edge going to the Patriots, who finished with 47 sacks (second in the league to the Chargers’ 42, which left them in fifth). In the vital area of interceptions, however, San Diego was substantially better, leading the league with 30 interceptions to New England’s 19 (good enough for only sixth in the league). Over their last eight games, the overall edge goes to San Diego, with 24 sacks to New England’s 23, and 17 interceptions to New England’s 10.

A Super Bowl between these two teams on a neutral site would promise to be the game of the year. For starters, the Chargers are strongest exactly where the Patriots are weakest. New England’s run defense is mediocre, and San Diego’s seasonal yards per rush average of 4.2 doesn’t take into account that when LaDainian Tomlinson, the league’s best runner, carries the ball, San Diego has the best running game in the NFL. Tomlinson averaged 4.7 yards per try in the regular season and just a fraction under five over the last eight games.

Of course, the reason opponents haven’t been able to take advantage of the Patriots’ problem with the run is that they spend most of the game passing to catch up. But San Diego’s three-four is capable of putting pressure on Tom Brady, while a ball-hawking defense — cornerback Antonio Cromartie has 10 interceptions and safeties Clinton Hart and Marlon McCree have eight between them — is better suited than any unit in the league to slow the Patriots down.

The all-important position of quarterback may seem like a mismatch, with Brady averaging 295 yards per game over his last eight, while the relatively inexperienced Philip Rivers has averaged just 207. Over the stretch, though, Brady hasn’t thrown better than Rivers so much as more, averaging 7.8 YPA to Rivers’s 7.7. And while New England would seem to have the better wide receivers, Rivers has perhaps the league’s best tight end in Antonio Gates — 75 receptions for an average of 13.1 yards per catch with nine TDs. This means that in key situations, Rivers could get excellent yardage on “safe” plays: quick passes to his tight end sliding off the line.

If I’ve given false hope to the dozen or so San Diego Chargers fans reading this, it’s time to burst your bubble. This Sunday’s game isn’t the Super Bowl, and it won’t be played on a neutral site. Not only are the Patriots playing at home; they’ll be playing a warm weather team in what looks to be arctic conditions. (It will be interesting, though, to see if the subzero weather puts a stick in the spokes of Brady’s passing and turns the game into more of a ground contest, where the Chargers have an advantage.)

Coaching and experience also heavily favor New England — but, of course, this was also true when the Chargers played the Colts, whom they beat during both the regular season and the playoffs.

San Diego’s real problem isn’t the weather or the experience: It’s their medical prognosis. As we go to press, the outlooks for Rivers, Tomlinson, and Gates — precisely the three players the Chargers can’t afford to have on the bench — aren’t good. And even if they play, it’s hard to believe they could play at the level of performance needed after missing practice nearly all week. And the bad news for Chargers hopefuls keeps on coming. Nose tackle Jamal Williams missed practice nearly all week with a bad ankle, and Shawne Merriman, the team’s sack leader with 12, has been sidelined with the flu.

For all these reasons, the 14 points the Pats are favored by would seem to be a safe bet. Still, if you turn on your TV Sunday afternoon and Rivers, Tomlinson, Gates, Williams, and Merriman are all in the lineup, don’t count the Chargers out. In mid-November, they were recognized as pro football’s biggest underachievers. Since then, they’ve been even more perfect than the Patriots.

Mr. Barra is the author of “The Last Coach: A Life of Paul ‘Bear’ Bryant.”